The dual conversion, four quadrant, linear solar concentration panel concept has been adopted to provide two dimension, or all around solar ray concentration on a three dimensional focal zone, rather than on a single focal line, as with a conventional parabolic linear reflector, with only two lower solar exposure quadrants.
The previously disclosed four quadrant, two dimensional linear concentration panels defined the geometric proportions and parameters, along with the total concentration ratio from all three reflective sections and one top row of linear convex lenses.
The prior solar panel's proportions were based on an assumed ideal panel width of 18", which is believed to be about the maximum width that can readily controlled during continuous oscillations, and resist damage from high wind and storm loads. It is possible that wider panels are practical, but the weight must be kept to a minimum consistant with structural rigidity and strength.
The key factor in the value of these latest solar panels is that solar concentration is provided in all four quadrnats of the focal zone, so that compact solar ray convergence is achieved with a high total concentration ratio. The classic type of linear parabolic reflector panel, used to heat water into steam was a shallow height, low ratio-(about 5:1) configuration.
The conventional parabolic reflectors provided solar ray concentration in less than two lower quadrants at the focal line, plus only one-sun exposure from the top, which necessitates the use of a very long pipe line in order to flash the hot water over to steam.
Some recent sun-tracking solar concentration panels provide only solar concentration from the top linear lens surface which, at best, provides a continuous heat transfer onto the top half of a focal line pipe. Aside from the heating loss at the unheated pipe underside, inordinate stresses are induced in the full pipe cross-section, with the top half expanding at a greater rate than the bottom half in the linear direction.
This latest type of high ratio deep contour linear concentrator panel is ideally matched to a combined steam flash boiler piping system, and localized square-form array of solar cells, because a cost/effective balance can be achieved--between the two methods which can result in the lowest possible cost-per-watt power output for home-sized power installations.
Although originally designed for use with central flash boiler pipes for a mechanical-to-electrical solar conversion system, the deep contoured, four quadrant solar panels are attractive for use with photovoltaic solar cells, when these are arrayed along, and in contact with, the flash boiler pipe, to produce a combined high density electrical power output, within a practical solar exposed total surface area.
The key point in the application of commercial silicon photovoltaic cells is that the optimum solar concentration ratio should be utilized, so that the highest possible wattage-to-cost output can be realized. Even though the linear watts-to concentration ratio is exceeded and lower proportional current is produced as the solar exposure increases, this inordinate current increase can be worthwhile for the system. Any disproportionate current increase can be cost-effective up to a high concentration ratio because the cost of the basic solar concentration panel is relatively inexpensive,--compared to current silicon photovoltaic solar cells.
When the arrays of solar cells are used with a central flash boiler pipe, the solar cells must be densely placed at the cold water entrance end of the panels, so that a cooling means is provided for the cells. The heat dissipated from the solar cells will provide the water pre-heating required for the later steam flashover near the exit end of the panels.
Essentially the combined solar cells and flash boiler piping solar conversion system requires that the multiple solar ar cells be located at the input cool water panel end for cooling purposes, and the flash boiler pipes exposed to high solar concentration for most of the piping length, and at the exit end of the panels, in a mutually compatible arrangement.
Although it may appear to be more logical to utilize increasing larger widths of full parabolic reflectors for corresponding larger solar concentration ratios, coupled with a small size of steam boiler pipe, there are several reasons for adopting a deep contour, four-quadrant concentration panel configuration place of the standard parabolic reflective section.
The key point against the linear parabolic reflective cross-section is there is an excessive lateral area solar collection loss because the section focal line is in line with the panel lateral lines, so that highly desirable solar concentration above the focal line is lost.
Another reason against the basic parabolic section is that it does not have the best possible structural section modulus when used for an elongate solar concentration panel.
A third, and final point against the basic parabolic cross-section is that the converging solar rays are focused on a thin line, rather than on a vertical plane surface, as represented by a flash boiler pipe, or line of solar cells at the focal zone. Additional equal and opposite concave side reflective extensions are necessary to provide uniform solar ray convergence on the second (height) dimension, as in the case of the present four quadrant, two dimensional solar concentration panels.
A major consideration in the application of any type of solar concentration panel is that the vertical centerline must always be kept in line with the normal solar rays, at any given time. The solar rays must fall normal to the horizontal axis of the panels, so that symmetrical, uniform solar ray distribution is maintained. These present solar concentration panels must track the sun within about one degree so that no inordinate dropoff in temperature and illumination occurs at the linear focal zone.
The linear solar concentrator panels are made of built-up fiber-glass-epoxy resin, on accurate cross-section forms. The panels are reinforced with longitudinal ribs and stringers, along with uniformly spaced cross partitions which also support the top linear lens sections and focal zone components.
The solar panels may be made up to about thirty feet in length, maximum, and may be fabricated in shorter five foot lengths which are joined together with formed metal slip-joint connectors to provide the total panel lengths required for each specific installation.
Each reflective concave surface of the panels must be fully mirrored, or have identical narrow mirror segments uniformly bonded to the continuous concave surface.
There are several differences between these and previous panel designs, the most significant being the higher side reflective extensions to increase the concentration ratio. Additionally, two equal and opposite lower reflective curved strips are located adjacent to the panel centerline, along with elongate slots on the centerline between each cross partition. The slots serve as rain drainage wind load relief means. so that somewhat wider solar panels are made possible.
This latest type of solar conversion power system is aimed at utilizing the operating features of both a flash boiler piping arrangement and series of solar photovoltaic cells to their best natural advantage, in a combined system to obtain the highest cost-effectiveness conversion possible on a final installation cost-per-watt output basis.